In this kind of MFM and MFC, a vertical positional relationship is not generated between a pair of thermal type sensors as far as a sensor arranged portion of a flow rate measuring conduit in a thermal type mass flow meter sensor portion is horizontal, a thermal siphon phenomenon is not generated, and a measurement error (an indication error) is not generated under the influence of the thermal siphon phenomenon.
However, there are many cases that it is necessary to install a main body block in such a vertical posture that a fluid flow path in an inner portion thereof has a perpendicular portion so as to use, based on a constructional relation of a piping system, a relation of an installation space of the MFM and MFC, or the like. At a time of installing and using in such a vertical posture or an inclined posture, since a pair of sensors of the flow rate measuring conduit in the thermal type mass flow sensor portion have a vertical positional relationship, a thermal siphon phenomenon is generated, so that an error is generated in a measurement result of the flow rate due to the influence.
As the MFM which is developed for the purpose of lowering the measurement error caused by the thermal siphon phenomenon mentioned above, there has conventionally known a structure made such that a pair of sensors are positioned within the same horizontal surface even in the case that a main body block is installed in a vertical posture, by interposing a flow path converting block converting a flow path in which a fluid flows at 90 degrees between the main body block and the thermal type mass flow sensor portion, and arranging the flow rate measuring conduit in the thermal type mass flow sensor portion orthogonal to a fluid flow path in an inner portion of the main body block (for example, refer to Patent Document 1).    Patent Document 1: Japanese Utility Model No. 2589318